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Z Diagram (z + diagram)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Imaging and spectroscopy of ultrasteep spectrum radio sources,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
Carlos G. Bornancini
ABSTRACT We present a sample of 40 ultrasteep spectrum (USS; ,,, 1.3, S,,,,) radio sources selected from the Westerbork in the Southern Hemisphere (WISH) catalogue. The USS sources have been imaged in K band at the Cerro Tololo Inter-American Observatory (CTIO) and with the Very Large Telescope (VLT) at Cerro Paranal. We also present VLT, Keck and William Herschel Telescope (WHT) optical spectroscopy of 14 targets selection from four different USS samples. For 12 sources, we have been able to determine the redshifts, including four new radio galaxies at z > 3. We find that most of our USS sources have predominantly small (<6 arcsec) radio sizes and faint magnitudes (K, 18). The mean K -band counterpart magnitude is . The expected redshift distribution estimated using the Hubble K,z diagram has a mean of , which is higher than the predicted redshift obtained for the Sydney University Molonglo Sky Survey,NRAO VLA Sky Survey (SUMSS,NVSS) sample and the expected redshift obtained in the 6C** survey. The compact USS sample analysed here may contain a higher fraction of galaxies which are high redshift and/or are heavily obscured by dust. Using the 74, 352 and 1400 MHz flux densities of a subsample, we construct a radio colour,colour diagram. We find that all but one of our USS sources have a strong tendency to flatten below 352 MHz. We also find that the highest redshift source from this paper (at z= 3.84) does not show evidence for spectral flattening down to 151 MHz. This suggests that very low frequency selected USS samples will likely be more efficient to find high redshift galaxies. [source]

The K - z diagram of FIRST radio sources identified in the Boötes and Cetus fields

ASTRONOMISCHE NACHRICHTEN, Issue 8 2009
K. El Bouchefry
Abstract This paper presents the Hubble diagram (K - z relation) for FIRST (Faint Images of the Radio Sky at 20 cm) radio sources identified in the Boötes and Cetus fields. The correlation between the K magnitude of the FIRST-NDWFS sample and the photometric redshifts found to be linear. The dispersion about the best fit line is given by 1.53 for the whole sample and 0.75 at z > 1. The paper also presents a composite K - z diagram of FIRST radio sources and low-frequency selected radio samples with progressively fainter flux-density limits (3CRR, 6C, 7CRS and the EIS-NVSS sample). The majority of FIRST radio sources lie fainter than the no evolution curve (3 L* galaxies) probably highlighting the fact that the galaxy luminosity is correlated with the radio power (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Identifications of FIRST radio sources in the NOAO Deep Wide-Field Survey

ASTRONOMISCHE NACHRICHTEN, Issue 6 2007
K. El Bouchefry
Abstract In this paper we present the results of an optical and near infrared identification of 514 radio sources from the FIRST survey (Faint Images of the Radio Sky Survey at Twenty centimetres) with a flux-density limit of 1 mJy in the NOAO Deep Wide-Field Survey (NDWFS) Boötes field. Using optical (Bw, R, I) and K band data with approximate limits of Bw , 25.5 mag, R , 25.8 mag, I , 25.5 mag and K , 19.4 mag, optical counterparts have been identified for 378 of 514 FIRST radio sources. This corresponds to an identification rate of 34% in four bands (BwRIK), 60% in optical bands (BwRI) and 74% in the I band. Photometric redshifts for these sources have been computed using the hyperz code. The inclusion of quasar template spectra in hyperz is investigated. We note that the photometric data are, in many cases, best matched to templates with very short star-formation timescales and the inferred ages of identified galaxies depend strongly on the assumptions about the star-formation timescale. The redshifts obtained are fairly consistent with those expected from the K - z relation for brighter radio sources but there is more scatter in the K - z diagram at z < 1. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]